Apply "source" attribute to jobs initiated by scan execution policy

When an SEP job is created, set the source value to scan_execution_policy

Some time ago our team had similar challenge in Set policies CI variables with the highest prec... (!135359 - merged)

SEP jobs are created/prepared in 2 places:

• when scheduled Scan Execution Policies are used, then we execute ee/app/services/security/security_orchestration_policies/create_pipeline_service.rb, although then the whole pipeline has a source configured as security_orchestration_policy, so it should be easy to set job_source to desired value there, as all jobs created in that service should be scan_execution_policy type,
• when regular pipeline Scan Execution Policies are used, then we use ee/lib/gitlab/ci/config/security_orchestration_policies/processor.rb to prepare job configuration, I believe this might be the place to set job_source and other desired values 🤔